1. Field of Invention
The present invention relates to a pattern on a mask and a method for forming the same. More particularly, the present invention relates to an anti-aberration pattern on a mask and a method for forming the same.
2. Description of Related Art
In the manufacture of integrated circuit, photolithography process is used to transfer patterns from a photo mask having customized circuit patterns to thin films formed on a wafer. The image transfer process comprises steps of forming a photoresist layer on a non-process layer, illuminating the photoresist layer through a photo mask having the customized circuit patterns, developing the photoresist layer and then etching the non-process layer by using the patterned photoresist layer as a mask. Hence, the image transfer process is accomplished.
However, the critical dimension of the pattern in the photoresist layer is affected by several factors including the exposure dosage, thickness of the photoresist layer and the variables in the development process. With the decrease of the size of the device, the line width of the device is getting smaller and smaller. Therefore, a small amount difference in the critical dimension of the device will lead to dramatic changes in electrical performance of the device. However, as the critical dimension of the device is decreased, the aberration caused by the photo tools strongly affects the appearance of the critical dimension of the dense pattern, especially the edge features of the dense pattern.
Currently, the way to alleviate the unbalanced developed critical dimensions of the edge features of the dense pattern is to sacrifice the performance of the photo tool to compensate the critical dimension difference. Nevertheless, as the critical dimension of the device is decreased, sacrificing the performance of the photo tools is not enough for balancing the developed critical dimension differences at the edge features of the dense pattern. Instead, the relatively poor photo tool performance ruin the reliability of the device.